BN_CTX_START(3) OpenSSL BN_CTX_START(3)NAME
BN_CTX_start, BN_CTX_get, BN_CTX_end - use temporary BIGNUM variables
void BN_CTX_start(BN_CTX *ctx);
BIGNUM *BN_CTX_get(BN_CTX *ctx);
void BN_CTX_end(BN_CTX *ctx);
These functions are used to obtain temporary BIGNUM variables from a
BN_CTX (which can been created by using BN_CTX_new(3)) in order to save
the overhead of repeatedly creating and freeing BIGNUMs in functions
that are called from inside a loop.
A function must call BN_CTX_start() first. Then, BN_CTX_get() may be
called repeatedly to obtain temporary BIGNUMs. All BN_CTX_get() calls
must be made before calling any other functions that use the ctx as an
Finally, BN_CTX_end() must be called before returning from the
function. When BN_CTX_end() is called, the BIGNUM pointers obtained
from BN_CTX_get() become invalid.
RETURN VALUESBN_CTX_start() and BN_CTX_end() return no values.
BN_CTX_get() returns a pointer to the BIGNUM, or NULL on error. Once
BN_CTX_get() has failed, the subsequent calls will return NULL as well,
so it is sufficient to check the return value of the last BN_CTX_get()
call. In case of an error, an error code is set, which can be obtained
SEE ALSOBN_CTX_new(3)HISTORYBN_CTX_start(), BN_CTX_get() and BN_CTX_end() were added in OpenSSL
OpenBSD 4.9 December 14, 2000